Cathode-ray-tube scanning circuit



.S pt. 21, 8- R. 1.. SNYDER, JR I 2,449,792

CATHODE-RAY TUBE SCANNING CIRCUIT Filed Jan. 31, 1946 F INVENTOR Richard L,S nyd er Jr.

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I ATTORNEY f atented Sept.

CATHODE-RAY TUBE SCANNING CIRCUIT Richard L. Snyder, Jr., Princeton, N. J assignor to Radio Corporation of America, a corporation of Delaware Application January 31, 1946, Serial No. 644,524

This invention relates to cathode ray scanning circuits, and has for its principal object the provision of an improved scanning circuit and method of operation whereby the electron beam of a cathode ray tube is made to scan the target of such a tube in a spiral path once for each pulse applied to the input of the scanning circuit.

In connection with the operation of pulse radar systems and other systems includin a cathode ray tube of the storage type, it is desirable (1) to deflect the electron beam of the tube over as long a path as possible in order to obtain maximum resolution of the values stored in the target, (2) to start the scanning cycle at any time a synchronizing pulse is applied to the input of the scanning circuit, (3) to follow the same scanning cycle without deviation each time a synchronizing pulse is applied, (4) to start the scanning cycle Within a few microseconds after the synchronizing pulse is received, and (5) to turn the beam on at the beginning of the scanning cycle and off at the end of this cycle in order to avoid fluctuations incident to the operation of the.

scanning circuit during its return to its normal standby condition.

For achieving these various results, there are provided three separate channels having a common input terminal to which the synchronizing pulses are applied. Two of these channels function to produce in the beam deflection coils of the cathode ray tube currents which are in quadrature, the current of one coil being zero and that of the other being a maximum when the starting pulse occurs so that there are produced in the separate deflecting coils oscillations which are 90 apart and gradually decrease in amplitude. This results in a rotating magnetic field by which the electron beam of the tube is constrained to move in a spiral path. The other of the three channels functions to bias ofl the electron beam at the end of the scanning cycle and to bias it on the beginning of the scanning cycle.

Important objects of the invention are the provision of an improved scanning system which completes one scanning cycle in response to the application of any single or isolated pulse, the

provision of a scanning circuit whichinitiates scanning of the target without appreciable time delay, and the provision of means whereby the effect of undesired fluctuations on the movement of the beam is avoided.

' The invention will be better understood from the following description considered in connection.

with the accompanying drawing and its scope is indicated by the appended claims.

Claims. (01. s 22) The. single figure of the drawing is a wiring diagram of a preferred form of the scanning circuit of the present invention.

This circuit includes an input terminal 20 which (1) is coupled through a capacitor 2| to a No. 1 channel which functions to produce in a beam deflecting coil 22 a current which is zero when time equals zero, (2) is coupled through a capacitor 23 to a No. 2 channel which functions to produce in a beam deflecting coil 24 a current which is a maximum when time equals zero, and (3) a No. 3 channel which functions to bias the beam of the tube 25 on and ofi at the beginning and end of the scanning cycle.

The No. 2 channel includes a slide back trigger circuit 26 of the multivibrator type, a cathode follower 21 and a pair of triodes 28 which function as a negative resistance. The cathodes of the cathode follower 28 are coupled through a capacitor 29 to one anode of the triodes 28 and are connected to the high voltage side of the beam deflecting coil 24. The low voltage side of the coil 24 is grounded through a lead 3|. Connected in shunt to the coil 24 are an adjustable capacitor 32 and any one of the capacitors 33, 34, 35, 36 or 3! which is selected by a movable contact arm 38. The coil 24 and the capacitors connected in parallel with it form a tuned circuit which is set into oscillation when current conductivity is transferred from the right hand triode to the left hand of the slide back trigger circuit 26, these oscillations being damped by the negative resistance element 28 so that their amplitude decreases in value.

Operating potential is applied from a 300 volt +B lead 38 through a common resistor 39 of 1000 ohms and separate resistors 40 and 4| each of 10,000 ohms to the anodes 42 and 43 of the slide back trigger circuit 26. The bias potential of the grid 44 is determined by the potentials across the resistors 45 of 1.8 megohms and 46 of 120,000 ohms. The cathode 41 is grounded through a 3300 ohm resistor 48. The grid 49 is connected to the cathode 41 through an adjustable 2 mego-hm resistor 50 and is coupled to the anode 42 through a 3300 microfarad capacitor 5|. The output lead 52 of the slideback trigger circuit 26 is coupled through a .01 microfarad capacitor 53 to the common terminal of a 2 megohm resister 54 and a 10,000 ohm resistor '55 which form the input to the cathode follower 27, The condition of the trigger circuit 26 is stable with current in the triode element 43-4941 as indicated by the arrow.

The cathode follower 21 has potential applied circuit 20. The cathode 63 is connected through a I lead 04; to'the high voltage side of the coil 24 and through the 0.1 ohm coupling capacitor 29 to the anode 65 of the negative resistance device 28 as previously indicated' When :the slide back multivibrator 2 6 is stable with current conductivity in its anode 43, the potential of the anode 02 is highly positive and current flows .(1) from the lead 33 through the resistor '58, the cathode follower 21, the lead 64, the coil 24 and the lead '3I to ground and (2) from the lead 64to the capacitor 32 and which ever of the capacitors 33 to 31 is connected in parallel with it. 'When ourrent conductivity is transferred to the anode 42, thecurrent of the coil is suddenly interrupted and oscillations are set up in the resonant circuit formed by the coil and the capacitors.

The negative resistance device 28' functions to damp the oscillations thus produced so that their amplitude gradually decreases frcm the first oi the oscillations to the last. The device .28 has potential applied from the lead 30' (1) to its anode 05 through a 2200 ohm resistor 65, a 5000 ohm resistor 60 andan 18,000 ohm resistor 01, (2) to its anode 60 through a 12,000 ohm resistor 60, (3) to its grid!!! through an. 820,000 ohm resistor 'H and a 56,000 ohm resistor 12,and (4) to its grid I -3 through a 1.8 megohm'resistor i5 and a 120,000 ohm resistor M. The grid 13 is coupled through a 1200 microfarad capacitor E to an adjustable contact of the resistor 06. The cathode TI is grounded through a1500' ohm resistor i8;

(1) the anode becomes more positive thereby producing an attenuated rise in the voltage of the grid '53, (2) the anode 68 takes more current, (3) the potential of the cathode I7 becomes more positive, (4) the anode 65 takes less current and (5) a more positive potential is applied to the coil 20. negative resistance across the coil 24. By-suitable adjustment of the potentiometer 06;, the apparent resistance of the circuit can be made either positive or negative so that the decrement of the resonant circuit formed by the parallel connected coil'and capacitors is-readily controlled over a wide range.

The No. 1 channel includes (1) a' bufifer amplifier T9 to the grid 00 of which the control pulse of the lead is applied through the 1000 ohm capacitor '21, a 100,000 grid leak resistor SI being connected between this grid and ground,

is in parallel with an adjustable capacitor 00.

and Whatever one of the capacitors 9| to 95. areselected by a movable contact arm 90. The coil 22 and the capacitors connected in parallel with it form a resonant circuit in which oscillations 90 out-of phase with-those ofthe resonant circuit 2432 are produced.

Thisregenerative action functions as a The buifer amplifier I9 has +B potential ap- .plied'to its anodes I00 and 83 through a 1000 I is adjustable.

ohm common resistor 97 and through individual resistors 98 and 99 each of 10,000 ohms. The cathode II is common to the two stages of the amplifier and is grounded through a 2200 ohm resistor I02 which is bypassed by a .01 ohm capacitor I 03. The grid I00 of the second ampliiier stage 03e-I04-IOI is coupled to the anode I00 through a 3300 microfarad capacitor I05 and is connected to ground through a 100,000 ohm resistor I00 and the parallel circuit formed by the resistor I02 and the capacitor I03. The amplifier "I0 functions to apply to the grids I01, I08 and I09 of; the cathode follower a pulse of the same polarity as that of the pulse applied to the lead 20. A 3.3 megohm grid leak resistor H0 is connected between the grids I01, I03 and I09 and ground.

From the +13 lead, potential is applied to the anodes Ill, H2, H3 and H4 of the cathode follower 82 through a 25,000 ohm resistor I 15 which When the amplified positive cut put pulse of the amplifier'lfl is applied to the grids I07, H28 and I09 of the cathode follower 82, the rise in the voltage of the cathodes 8! and 88 is so sudden that little or no current flows in the coil 22 andall the energy is stored in the capacitors connected in parallel with this coil.

The resulting oscillations are damped by the neg- 'ative resistance device 85 as explained in connection' with the device 28.

It will be noted that the common anode terminals of the units 26, I9 and, 82 are bypassed to ground respectively through a 1 microfarad imizing the undesired effect, of extraneous fluctu- When the voltage at the high side: of the coil 24 is increased, as previously explained;

ations in the potentials at these points.

For damping the oscillations between scanning cycles, the positive pulse produced at the anode of the unit 25 is applied through (1) a filter network including a 100 microfarad capacitor IIBand a 68,000 ohm resistor I20, (2) a 1000 microfarad coupling capacitor HI, and a filter network including a 330,000 ohm resistor E22 and a 3.3 megohm resistor I23 and a .01 microfarad capacitor I24 to the grid I 25 of the triode element IMI25--'88 which has its cathode 88 connected to the free side of the beam deflecting coil 22.

With these connections, the positive wave delivered from the anode 42 is distorted so that it rises to a maximum and radually decreases. This causes the current of the triode I! 4I 25,88 to rise suddenly damping the oscillations in the resonant circuit formed by the coil 22 and its deflecting coils 22, and 24 and. the frequency at which the target of the cathode ray tube is-to be. scanned.

From what has been said, it is apparent that the two resonant circuits (1) are tuned to the 'same frequency, (.2) are damped at. the same rate, and (3) function together to produce a rotating deflecting magnetic field which grade ua lly decreases in amplitude and causes the. electron beam to scan the target in a. spiral path.

Otherwise stated, the positive timing pulse ap plied to the lead 'always occurs with the current in the coil 22 at its Zero value and that in the coil 24 at its maximum value so that current begins to be delivered to the coil 22 from its parallel-connected capacitors and current is delivered from the coil 24 to its parallel-connected capacitors, thus producing in the two tuned circuits oscillations which have the same frequency and differ in phase by 90.

At the end of each scanning cycle, the electron beam is biased oif by means of the No.3 channel which includes (1) a slide back trigger circuit I26 similar to the trigger circuit 26 of the No. 2 channel and (2) a double rectifier unit I21. The various details of the trigger circuit I26 are apparent from what has been said in connection with the similar trigger circuit 26. In each case, the trigger circuit is stable only with current conductivity in the right hand anode and is transferred temporarily to the left hand anode in response to application of a positive pulse to the lead 20. After a time interval predetermined by adjustment of the grid resistor 50 or I28, current conductivity automatically returns to the right hand anode. The unit I26 is adjusted to return current conductivity to the right hand anode slightly in advance of the return of conductivity to the anode 43 so that the beam is biased off before any extraneous disturbances occur in the deflecting circuits. The beam is biased on in response to a positive pulse applied to a .01 ohm coupling capacitor I29 and is biased oiT in response to a negative pulse applied to this coupling capacitor.

These beam biasing pulses are applied (1) through a .01 microfarad capacitor I30, a 560,000 ohm resistor I3 I and a .01 microfarad coupling capacitor I32 to the beam control grid I33 of the cathode ray tube 25, and (2) through a 560,000 ohm resistor I34 to the cathode ray tube cathode I35 which is bypassed to ground by a 0.1 microfarad capacitor I36.

The purpose of the double rectifier I3II38 and I39I40 is to prevent overshooting when the beam is turned on and to provide a constant bias potential for the beam during the scanning cycle. This bias potential is provided by a network which includes the resistor I34, a 0.1 microfarad capacitor I4I connected between the upper end of the resistor I34 and the anode I31 and a 1 megohm resistor I'42 having an adjustable contact which is connected to the cathode I40 and is also connected through a 0.1 microfarad capacitor I43 to the cathode I35 of the cathode ray tube 25 which is bypassed to ground by capacitor I36. When a negative pulse is applied through the coupling capacitor I20, the cathode I38 pulls the anode I37 negative thus charging the capacitor MI and establishing a negative bias voltage across the resistor I42. If the beam tends to overshoot, the potential across the resistor I3I increases, the diode I39-I40 draws some current through a 1 megohm resistor I44 and the swing of the beam is retarded or stopped. The distributed capacity of the system is sufficient to round off any sudden changes which might otherwise shock into oscillation the sensitive amplifier system to which the output of the cathode ray storage device is connected.

What the invention provides is a scanning system which responds to a single positive pulse to execute only one scanning cycle wherein the beam moves over the target in a spiral path. While the invention is disclosed as applied to a oscillations in the first-of said tuned circuits," means responsive to said electrical pulse producing in the second of said tuned circuits oscillations which are in quadrature with the oscillations of said first tuned circuit, and means responsive to said electrical pulse for biasing ofi the ray of said tube at the end of a predetermined number of said oscillations.

2. The combination of a cathode ray tube having a cathode and a ray control grid and a pair T of ray deflecting coils, a pair of tuned circuits each including a different one of said coils, means'responsive to an electrical pulse for producing 05- cillations in the first of said tuned circuits, means responsive to said electrical pulse for producing in the second of said tuned circuits oscillations which are in quadrature with the oscillations of said first tuned circuit, and a network intercon-j necting said means for terminating the oscillations in one of said tuned circuits at a predeter-.

mined time after the occurrence of said electrical pulse.

3.'The combination of a cathode ray device wherein the intensity of a cathode ray is controlled by a grid and the position of said ray is.

controlled by vertical and horizontal ray deflecting coils, two groups of capacitors, simultaneously operated means for selectively connecting the capacitors of one of said groups in parallel with one of said coils to form a first tuned circuit and the capacitors of the second of said groups in parallel with the other of said coils to form a second tuned circuit, means for applying an electrical pulse, means responsive to said pulse for,

shock exciting said tuned circuits to produce in said coils currents which are in quadrature, and

means for attenuating said currents at the same rate.

4. The combination of a cathode ray device wherein the intensity of a cathode ray is controlled by a grid and the position of said ray is controlled by vertical and horizontal ray deflecting coils, two groups of capacitors, simultaneously operated means for selectively connecting the capacitors of one of said groups in parallel with one of said coils to form a first tuned circuit and the capacitors of the second of said groups in parallel with the other of said coils to form a second tuned circuit, means for applying an electrical pulse, means responsive to said pulse for shock exciting said tuned circuits to produce in said coils currents which are in quadrature, means for attenuating said currents at the same rate, and means responsive to said pulse for biasing on said ray only during the fiow of said currents.

5. The combination of a pair of coils arranged to produce a rotating magnetic field in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a difierent one of said coils to form first and second tuned circuits, means for applying an electrical pulse, and means responsive to said pulse for shock exciting said 7' tuned circuits to produce in them currents; which arein quadrature with one anothen i 6. The combination of a pair of coils arranged.

to produce a rotating magnetic field in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a different one of said coils to form first and second tuned circuits, means for applying an electrical pulse, means responsive to said pulse for shock exciting said tuned circuits to produce in them currents which are in quadrature with one another, and means for attenuating said currents at the same rate.

'7. The combination of a pair of coils arranged to produce a rotating magnetic field in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a different one of said coils to formfirst and second tuned circuits, means for applying an electrical pulse, means responsive to said pulse for shock exciting said tuned circuits to produce in them currents which are in quadrature with one another, and simultaneously operated means for adjusting the value of the capacitances connected across said coils so that said circuits are always tuned to the same frequency.

.8. The combination of a pair of coils arranged to produce a rotating magnetic field in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a different one of said coils to form first and second tuned circuits, means for applying an electrical pulse, first and second cathode followers each having its cathode connected to the freeside of a different one of said tuned circuits, a trigger circuit responsive to said pulse for deenergizing said first cathode follower during a predetermined time interval, and amplifying means responsive to said pulse for energizing said second cathode follower during said time interval.

9. The combination of a pair of coils arranged to produce a rotating magnetic field, in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a different one of said coils to form first and second tuned circuits, mean-s for applying an electrical pulse, first and second cathode followers each having its cathode coin nected to the free side of a. different one of said tuned circuits, a trigger circuit responsive to said pulse for deenergizing said first cathode follower during a predetermined time interval, amplifying means responsive to said pulse for energizing said second cathode follower during said time interval, and means for attenuating the currents of said coils at the same rate.

10. The combination of a pair of coils arranged to produce a rotating magnetic field in response to currents in quadrature with one another, first and second capacitance means each arranged to be connected across a different one of said coils to form first and second tuned circuits, means for applying an electrical pulse, first and second cathode followers each having its cathode connected to the free side of a different one of said tuned circuits, a trigger circuit responsive to said pulse for deenergizing said first cathode follower during a predetermined time interval, amplifying means responsive to said pulse for energizing said .secondcathode follower during said time interval, and means connected between the second of said cathode followers and said trigger circuit. for attenuating oscillations tending to occur after the expiration of said time interval.

RICHARD L. SNYDER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,103,090 Plebanski Dec. 21, 1937 2,153,202 Nichols Apr. 4, 193-9 2,266,668 Tubbs Dec. 16, 1941 2,307,237 Rea et a1 Jan. 5, 1943 2,364,756 Roberts Dec. 12, 1944 2,370,685 Rea et al. Mar. 6, 1945 2,408,414 Donaldson Oct. 1, 1946 2,408,415 Donaldson Oct. 1, 1946 2,412,291 Schade Dec, 10, 1946 FOREIGN PATENTS Number Country Date 406,903 Great Britain Mar. 8, 1934 

